One often overlooked source of vac leaks the intake manifold bolts. They become loose with time and slowly start causing odd running issues. Easy to check, just put a small wrench on and see if the bolt can be hand tightened a few pounds. Go around to all of them as the one you miss is the one that is loose.

Good call.

One of the nuts on #4 was so loose that I turned it by hand. One of the #6 nuts turned 1/4 turn with a wrench; others on that side were ok. May have to remove the IC to get to the 1-3 bolts. Yet another weekend job.